U.S. patent application number 12/174034 was filed with the patent office on 2009-03-26 for electrode for fuel cell and fuel cell system including same.
Invention is credited to Hyun-Seok Cho, Ji-Seok Hwang, You-Mee Kim, Hyoung-Seok Song, Min-Kyu Song.
Application Number | 20090081526 12/174034 |
Document ID | / |
Family ID | 40471991 |
Filed Date | 2009-03-26 |
United States Patent
Application |
20090081526 |
Kind Code |
A1 |
Hwang; Ji-Seok ; et
al. |
March 26, 2009 |
ELECTRODE FOR FUEL CELL AND FUEL CELL SYSTEM INCLUDING SAME
Abstract
An electrode for a fuel cell and a fuel cell system including
the electrode. The electrode includes an electrode substrate
including carbon fiber and a hydrophobic polymer fiber, and a
catalyst layer on the electrode substrate. As such, the electrode
uniformly includes the hydrophobic polymer fiber thereon, and
therefore can uniformly release and maintain water generated during
operation of the fuel cell, thereby improving fuel cell
characteristics.
Inventors: |
Hwang; Ji-Seok; (Suwon-si,
KR) ; Song; Min-Kyu; (Suwon-si, KR) ; Kim;
You-Mee; (Suwon-si, KR) ; Song; Hyoung-Seok;
(Suwon-si, KR) ; Cho; Hyun-Seok; (Suwon-si,
KR) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Family ID: |
40471991 |
Appl. No.: |
12/174034 |
Filed: |
July 16, 2008 |
Current U.S.
Class: |
429/450 |
Current CPC
Class: |
H01M 8/0234 20130101;
H01M 8/0239 20130101; H01M 8/0243 20130101; H01M 2008/1095
20130101; H01M 8/1004 20130101; H01M 4/8605 20130101; Y02E 60/50
20130101 |
Class at
Publication: |
429/40 |
International
Class: |
H01M 4/00 20060101
H01M004/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 20, 2007 |
KR |
10-2007-0096105 |
Claims
1. An electrode for a fuel cell comprising: an electrode substrate
comprising a carbon fiber and a hydrophobic polymer fiber; and a
catalyst layer on the electrode substrate.
2. The electrode of claim 1, wherein the hydrophobic polymer fiber
is weaved with the carbon fiber.
3. The electrode of claim 1, wherein the hydrophobic polymer fiber
has an average diameter ranging from about 100 nm to about 10
.mu.m.
4. The electrode of claim 3, wherein the hydrophobic polymer fiber
has the average diameter ranging from about 100 nm to about 1
.mu.m.
5. The electrode of claim 1, wherein the carbon fiber and the
hydrophobic polymer fiber are mixed in a ratio ranging from about
99:1 to about 50:50 wt %.
6. The electrode of claim 5, wherein the carbon fiber and the
hydrophobic polymer fiber are mixed in the ratio ranging from about
95:5 to about 80:20 wt %.
7. The electrode of claim 1, wherein the hydrophobic polymer fiber
comprises a resin selected from the group consisting of
polytetrafluoroethylene, polyvinylidene fluoride,
polyhexafluoropropylene, polyperfluoro alkylvinylether,
polyperfluorosulfonylfluoride, alkoxyvinyl ether, fluorinated
ethylene propylene, polychlorotrifluoroethylene, copolymers
thereof, and combinations thereof.
8. A fuel cell system comprising: at least one electrical generator
comprising a membrane-electrode assembly and generating electricity
through electrochemical reaction of a fuel and an oxidant, the
membrane-electrode assembly comprising an anode, a cathode facing
the anode, and a separator between the anode and the cathode, at
least one of the anode or the cathode comprising an electrode
substrate and a catalyst layer; a fuel supplier supplying the at
least one electrical generator with a fuel; and an oxidant supplier
supplying the electrical generator with an oxidant, wherein the
electrode substrate comprises a carbon fiber and a hydrophobic
polymer fiber.
9. The fuel cell system of claim 8, wherein the hydrophobic polymer
fiber is weaved with the carbon fiber.
10. The fuel cell system of claim 8, wherein the hydrophobic
polymer fiber has an average diameter ranging from about 100 nm to
about 10 .mu.m.
11. The fuel cell system of claim 10, wherein the hydrophobic
polymer fiber has the average diameter ranging from about 100 nm to
about 1 .mu.m.
12. The fuel cell system of claim 8, wherein the carbon fiber and
the hydrophobic polymer fiber are mixed in a ratio ranging from
about 99:1 to about 50:50 wt %.
13. The fuel cell system of claim 12, wherein the carbon fiber and
the hydrophobic polymer fiber are mixed in the ratio ranging from
about 95:5 to about 80:20 wt %.
14. The fuel cell system of claim 8, wherein the hydrophobic
polymer fiber comprises a resin selected from the group consisting
of polytetrafluoroethylene, polyvinylidene fluoride,
polyhexafluoropropylene, polyperfluoroan alkylvinylether,
polyperfluorosulfonylfluoride, alkoxyvinyl ether, fluorinated
ethylene propylene, polychlorotrifluoroethylene, copolymers
thereof, and combinations thereof.
15. A fuel cell electrode comprising: an electrode substrate
comprising a hydrophobic polymer fiber weaved with a carbon fiber;
and a catalyst layer on the electrode substrate.
16. The electrode of claim 15, wherein the hydrophobic polymer
fiber has an average diameter ranging from about 100 nm to about 10
.mu.m.
17. The electrode of claim 16, wherein the hydrophobic polymer
fiber has the average diameter ranging from about 100 nm to about 1
.mu.m.
18. The electrode of claim 15, wherein the carbon fiber and the
hydrophobic polymer fiber are mixed in a ratio ranging from about
99:1 to about 50:50 wt %.
19. The electrode of claim 18, wherein the carbon fiber and the
hydrophobic polymer fiber are mixed in the ratio ranging from about
95:5 to about 80:20 wt %.
20. The electrode of claim 15, wherein the hydrophobic polymer
fiber comprises a resin selected from the group consisting of
polytetrafluoroethylene, polyvinylidene fluoride,
polyhexafluoropropylene, polyperfluoro alkylvinylether,
polyperfluorosulfonylfluoride, alkoxyvinyl ether, fluorinated
ethylene propylene, polychlorotrifluoroethylene, copolymers
thereof, and combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2007-0096105, filed in the Korean
Intellectual Property Office, on Sep. 20, 2007, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an electrode for a fuel
cell and a fuel cell system including the same.
[0004] 2. Description of the Related Art
[0005] A fuel cell system (or fuel cell) is a power generation
system for producing electrical energy through an electrochemical
redox reaction of an oxidant and a fuel, such as hydrogen or a
hydrocarbon-based material, such as methanol, ethanol, natural gas,
and the like. In addition, a fuel cell system is a clean energy
source that can replace systems using fossil fuels (or fossil fuel
type power generation systems). A fuel cell system includes a stack
composed of unit cells and produces various ranges of power output.
Since a fuel cell system has from about four to about ten times
more energy density than a small lithium battery, it has been
spotlighted as a small portable power source that can replace
lithium battery.
[0006] Representative exemplary fuel cell systems include a polymer
electrolyte membrane fuel cell (PEMFC) system and a direct
oxidation fuel cell (DOFC) system. The direct oxidation fuel cell
includes a direct methanol fuel cell that uses methanol as a fuel.
The polymer electrolyte fuel cell has relatively high energy
density and high power, but needs careful handling of hydrogen gas
and accessory facilities such as a fuel reforming processor for
reforming methane or methanol, natural gas, and the like in order
to produce the hydrogen gas as a fuel.
[0007] In contrast, a direct oxidation fuel cell has lower energy
density than that of the polymer electrolyte fuel cell, but it uses
a liquid-type fuel that can be easily handled, has a low operation
temperature, and needs no additional fuel reforming processor. In
the above-mentioned fuel cell system, a stack that substantially
generates electricity includes several to scores of unit cells
stacked adjacent to one another, and each unit cell is formed of a
membrane-electrode assembly (MEA) and a separator (also referred to
as a bipolar plate).
[0008] The membrane-electrode assembly is composed of an anode
(also referred to as a "fuel electrode" or an "oxidation
electrode") and a cathode (also referred to as an "air electrode"
or a "reduction electrode") that are separated by a polymer
electrolyte membrane. Electricity is generated as follows. A fuel
is supplied to the anode and adsorbed on catalysts of the anode,
and then oxidized to produce protons and electrons. The electrons
are transferred into the cathode via an external circuit, and the
protons are transferred into the cathode through the polymer
electrolyte membrane. In addition, an oxidant is supplied to the
cathode. Then the oxidant, protons, and electrons react with one
another on catalysts of the cathode to produce electricity along
with water.
SUMMARY OF THE INVENTION
[0009] Aspects of embodiments of the present invention are directed
toward a fuel cell electrode that is subjected to a uniform
water-repellent treatment, and/or that is capable of improving fuel
cell performance; and a fuel cell system including the same and/or
having positive fuel cell characteristics.
[0010] An embodiment of the present invention provides an electrode
for a fuel cell that includes an electrode substrate including a
carbon fiber and a hydrophobic polymer fiber, and a catalyst layer
on the electrode substrate.
[0011] Another embodiment of the present invention provides a fuel
cell system that includes at least one electricity generating
element (or electrical generator) including a membrane-electrode
assembly and generating electricity through electrochemical
reaction of a fuel and an oxidant, the membrane-electrode assembly
including an anode, a cathode facing the anode, and a separator
interposed between the anode and the cathode, at least one of the
anode or the cathode including an electrode substrate and a
catalyst layer; a fuel supplier supplying the at least one
electricity generating element with a fuel; and an oxidant supplier
supplying the electricity generating element with an oxidant. Here,
the electrode substrate includes a carbon fiber and a hydrophobic
polymer fiber.
[0012] Since a hydrophobic polymer is uniformly included on an
electrode substrate as a fiber according to an embodiment of the
present invention, the electrode substrate can uniformly maintain
and discharge water generated during operation of a fuel cell,
thereby improving fuel cell characteristics.
BRIEF DESCRIPTION OF THE DRAWING
[0013] The accompanying drawing, together with the specification,
illustrate exemplary embodiments of the present invention, and,
together with the description, serve to explain the principles of
the present invention.
[0014] FIG. 1 is a drawing showing an electrode substrate (a) in
which a carbon fiber is weaved with a hydrophobic polymer fiber, as
well as an enlarged drawing (b) of the electrode substrate (a);
and
[0015] FIG. 2 is a schematic view showing a fuel cell system
according to an embodiment of the present invention.
DETAILED DESCRIPTION
[0016] In the following detailed description, only certain
exemplary embodiments of the present invention are shown and
described, by way of illustration. As those skilled in the art
would recognize, the invention may be embodied in many different
forms and should not be construed as being limited to the
embodiments set forth herein. Also, in the context of the present
application, when an element is referred to as being "on" another
element, it can be directly on the another element or be indirectly
on the another element with one or more intervening elements
interposed therebetween. Like reference numerals designate like
elements throughout the specification.
[0017] An embodiment of the present invention relates to an
electrode for a fuel cell, and particularly to an electrode
substrate. In a fuel cell, an electrode substrate plays a role of
supporting an electrode and diffusing a fuel and an oxidant into a
catalyst layer so that the fuel and the oxidant can easily reach
the catalyst layer, and also of collecting a current generated from
the catalyst layer and delivering the current to a separator.
[0018] A conventional electrode substrate includes a conductive
material. For example, the electrode substrate includes carbon
paper, carbon cloth, or carbon felt.
[0019] In addition, the electrode substrate is treated with a
water-repellent in order to prevent (or reduce) diffusion
efficiency deterioration of a reactant due to water generated
during operation of a fuel cell.
[0020] The water-repellent treatment is performed by repeatedly
depositing a fluorine-base resin emulsion on a conductive substrate
to regulate the loading amount of the fluorine-based resin.
However, since the carbon paper, carbon cloth, or carbon felt is
formed of carbon fiber with high hygroscopicity, it is difficult to
uniformly disperse a fluorine-based resin on an electrode substrate
as well as to regulate the loading amount thereof. As such, the
electrode substrate may not be capable of uniformly releasing water
generated from the electrode during operation of a fuel cell. As a
result, the electrode may be flooded by water, which increases mass
transfer resistance of a reactant and thereby deteriorates cell
performance.
[0021] An embodiment of the present invention provides an electrode
for a fuel cell not having the above problem.
[0022] According to an embodiment of the present invention, an
electrode for a fuel cell includes an electrode substrate and a
catalyst layer disposed thereon. The electrode substrate includes a
carbon fiber and a hydrophobic polymer fiber. The carbon 10 fiber
is weaved with the hydrophobic polymer fiber, as shown in (a) of
FIG. 1 and enlarged drawing ((b) of FIG. 1) thereof.
[0023] The hydrophobic polymer fiber has an average diameter
ranging from about 100 nm to about 10 .mu.m (or from 100 nm to 10
.mu.m). In another embodiment, the hydrophobic polymer fiber has an
average diameter ranging from about 100 nm to about 1 .mu.m (or
from 100 nm to 1 .mu.m). In one embodiment, the hydrophobic polymer
fiber with an average diameter ranging from 100 nm to 10 .mu.m can
accomplish the desirable water repellency.
[0024] According to an embodiment of the present invention, unlike
a hydrophobic polymer fiber, the average diameter of a carbon fiber
does not have much influence on water repellency.
[0025] The carbon fiber may be mixed with the hydrophobic polymer
fiber in a ratio ranging from about 99:1 to about 50:50 wt % (or
from 99:1 to 50:50 wt %). In another embodiment, the mixing ratio
ranges from about 95:5 to about 80:20 wt % (or from 95:5 to 80:20
wt %). In one embodiment, when the hydrophobic polymer fiber is
included in an amount ranging from 1 to 50 wt %, the hydrophobic
polymer fiber can contribute to water repellency by regulating a
water-repellent treatment rate.
[0026] The hydrophobic polymer fiber may include, but is not
limited to, a fiber including a resin selected from the group
consisting of polytetrafluoroethylene, polyvinylidene fluoride,
polyhexafluoropropylene, polyperfluoroalkylvinylether,
polyperfluorosulfonylfluoride alkoxyvinyl ether, fluorinated
ethylene propylene, polychlorotrifluoroethylene, copolymers
thereof, and combinations thereof.
[0027] A conventional depositing method has caused a problem of not
uniformly discharging water, because a fluorine-based resin is
variably loaded in a depth direction. Accordingly, an embodiment of
the present invention provides an electrode substrate prepared by
weaving a hydrophobic polymer fiber, so that the hydrophobic
polymer can be uniformly included even in a depth direction. In
addition, when a fluorine-based resin is conventionally deposited
on an electrode substrate, there is a problem that the
fluorine-based resin cannot be uniformly distributed thereon.
However, when an electrode substrate of an embodiment of the
present invention is prepared by weaving a hydrophobic polymer with
a carbon fiber, the hydrophobic polymer can be uniformly
distributed, thereby providing a uniform water-discharge rate for
the electrode substrate.
[0028] In addition, a microporous layer (MPL) can be added between
the aforementioned electrode substrate and a catalyst layer to
increase reactant diffusion effects. The microporous layer
generally includes conductive powders with a certain (or set)
particle diameter. The conductive material of the microporous layer
may include, but is not limited to, carbon powder, carbon black,
acetylene black, ketjen black, activated carbon, carbon fiber,
fullerene, nano-carbon, or combinations thereof. The nano-carbon
may include a material such as carbon nanotubes, carbon nanofiber,
carbon nanowire, carbon nanohorns, carbon nanorings, or
combinations thereof.
[0029] The microporous layer is formed by coating a composition
including a conductive powder, a binder resin, and a solvent on the
conductive substrate. The binder resin may include, but is not
limited to, polytetrafluoroethylene, polyvinylidenefluoride,
polyhexafluoropropylene, polyperfluoro alkylvinylether,
polyperfluorosulfonylfluoride, alkoxyvinyl ether, polyvinylalcohol,
cellulose acetate, or copolymers thereof. The solvent may include,
but is not limited to, an alcohol such as ethanol, isopropyl
alcohol, n-propyl alcohol, butanol, and so on, water, dimethyl
acetamide, dimethyl sulfoxide, N-methylpyrrolidone, and/or
tetrahydrofuran. The coating method may include, but is not limited
to, screen printing, spray coating, doctor blade methods, gravure
coating, dip coating, silk screening, painting, and so on,
depending on the viscosity of the composition.
[0030] The catalyst layer can include any suitable catalyst for
participating in a fuel cell reaction, for example a platinum-based
catalyst. The platinum-based catalyst may be platinum, ruthenium,
osmium, a platinum-ruthenium alloy, a platinum-osmium alloy, a
platinum-palladium alloy, and/or a platinum-M alloy (wherein M is
at least one transition element selected from the group consisting
of Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh, and Ru).
As mentioned above, an anode and a cathode may include the same
material. However, a direct oxidation fuel cell may include a
platinum-ruthenium alloy catalyst as an anode catalyst in order to
prevent (or reduce) catalyst poisoning due to CO generated during
the anode reaction. Representative examples of the catalysts
include Pt, Pt/Ru, Pt/W, Pt/Ni, Pt/Sn, Pt/Mo, Pt/Pd, Pt/Fe, Pt/Cr,
Pt/Co, Pt/Ru/W, Pt/Ru/Mo, Pt/RuN, Pt/Fe/Co, Pt/Ru/Rh/Ni, and/or
Pt/Ru/Sn/W.
[0031] Such a catalyst may be used in a form as a metal itself
(black catalyst), or can be used while being supported on a
carrier. The carrier may include carbon such as graphite, denka
black, ketjen black, acetylene black, carbon nanotubes, carbon
nanofiber, carbon nanowire, carbon nanoballs, activated carbon, and
so on, or an inorganic material (or particulate) such as alumina,
silica, zirconia, titania, and so on. In one embodiment, the
carrier is formed using carbon. A noble metal supported on a
carrier may be a commercially available one or can be prepared by
supporting a noble metal on a carrier. A suitable method is used
for supporting the noble metal on the carrier.
[0032] The catalyst layer may further include a binder resin to
improve its adherence and proton transfer properties.
[0033] The binder resin may be a proton conductive polymer resin
having a cation exchange group selected from the group consisting
of a sulfonic acid group, a carboxylic acid group, a phosphoric
acid group, a phosphonic acid group, and derivatives thereof at its
side chain. Non-limiting examples of the polymer of the binder
resin include at least one proton conductive polymer selected from
the group consisting of perfluoro-based polymers,
benzimidazole-based polymers, polyimide-based polymers,
polyetherimide-based polymers, polyphenylenesulfide-based polymers
polysulfone-based polymers, polyethersulfone-based polymers,
polyetherketone-based polymers, polyether-etherketone-based
polymers, and polyphenylquinoxaline-based polymers. In one
embodiment, the proton conductive polymer is at least one proton
conductive polymer selected from the group consisting of
poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a
copolymer of tetrafluoroethylene and fluorovinylether having a
sulfonic acid group, defluorinated polyetherketone sulfide, aryl
ketone, poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole), and
poly(2,5-benzimidazole).
[0034] The hydrogen (H) in the cation exchange group of the proton
conductive polymer can be substituted with Na, K, Li, Cs, or
tetrabutylammonium. When the H in the cation exchange group of the
terminal end of the proton conductive polymer side chain is
substituted with Na or tetrabutylammonium, NaOH or
tetrabutylammonium hydroxide may be used during preparation of the
catalyst composition, respectively. When the H is substituted with
K, Li, or Cs, suitable compounds for the substitutions may be
used.
[0035] The binder resins may be used singularly or in combination.
They may be used along with non-conductive polymers to improve
adherence with a polymer electrolyte membrane. The binder resins
may be used in a controlled amount to adapt to their purposes.
[0036] Non-limiting examples of the non-conductive polymers include
polytetrafluoroethylene (PTFE),
tetrafluoroethylene-hexafluoropropylene copolymers (FEP),
tetrafluoroethylene-perfluoro alkylvinylether copolymers (PFA),
ethylene/tetrafluoroethylene (ETFE),
chlorotrifluoroethylene-ethylene copolymers (ECTFE),
polyvinylidenefluoride, polyvinylidenefluoride-hexafluoropropylene
copolymers (PVdF-HFP), dodecylbenzenesulfonic acid, sorbitol, and
combinations thereof.
[0037] According to one embodiment of the present invention, an
electrode for a fuel cell can be used as an anode or a cathode in a
membrane-electrode assembly. According to another embodiment of the
present invention, a membrane-electrode assembly includes an anode
and a cathode, and a polymer electrolyte membrane interposed
between the cathode and the anode.
[0038] The anode and/or the cathode may have the electrode
structure as above.
[0039] The polymer electrolyte membrane functions as an
ion-exchange member to transfer protons generated in an anode
catalyst layer to a cathode catalyst layer. In one embodiment, the
polymer electrolyte membrane of the membrane-electrode assembly
includes a proton conductive polymer resin. The proton conductive
polymer resin may be a polymer resin having a cation exchange group
selected from the group consisting of a sulfonic acid group, a
carboxylic acid group, a phosphoric acid group, a phosphonic acid
group, and derivatives thereof, at its side chain.
[0040] Non-limiting examples of the polymer resin include
fluoro-based polymers, benzimidazole-based polymers,
polyimide-based polymers, polyetherimide-based polymers,
polyphenylenesulfide-based polymers polysulfone-based polymers,
polyethersulfone-based polymers, polyetherketone-based polymers,
polyether-etherketone-based polymers, and
polyphenylquinoxaline-based polymers. In one embodiment, the proton
conductive polymer of the polymer resin is at least proton
conductive polymer selected from the group consisting of
poly(perfluorosulfonic acid) (NAFION.TM.), poly(perfluorocarboxylic
acid), a copolymer of tetrafluoroethylene and fluorovinylether
having a sulfonic acid group, defluorinated polyetherketone
sulfide, aryl ketone,
poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole), and
poly(2,5-benzimidazole). The hydrogen (H) in the proton conductive
group of the proton conductive polymer can be substituted with Na,
K, Li, Cs, or tetrabutylammonium. When the H in the ionic exchange
group of the terminal end of the proton conductive polymer side is
substituted with Na or tetrabutylammonium, NaOH or
tetrabutylammonium hydroxide may be used, respectively. When the H
is substituted with K, Li, or Cs, suitable compounds for the
substitutions may be used.
[0041] In one embodiment of the present invention, a fuel cell
system including the above described membrane-electrode assembly
also includes at least one electricity generating element (or
electrical generator), a fuel supplier, and an oxidant
supplier.
[0042] The electricity generating element includes a
membrane-electrode assembly and a separator. The membrane-electrode
assembly includes a polymer electrolyte membrane, and a cathode and
an anode disposed at opposite sides of the polymer electrolyte
membrane. The electricity generating element generates electricity
through oxidation of a fuel and reduction of an oxidant.
[0043] The fuel supplier plays a role of supplying the electricity
generating element with a fuel. The oxidant supplier plays a role
of supplying the electricity generating element with an oxidant
such as oxygen or air.
[0044] The fuel includes liquid or gaseous hydrogen, or a
hydrocarbon-based fuel such as methanol, ethanol, propanol,
butanol, or natural gas.
[0045] FIG. 2 is a schematic structure of a fuel cell system that
will be described in more detail. FIG. 2 illustrates a fuel cell
system wherein a fuel and an oxidant are provided to an electricity
generating element (or electrical generator) through pumps, but the
present invention is not limited to such structures. The fuel cell
system according to an embodiment of the present invention
alternatively includes a structure wherein a fuel and an oxidant
are provided in a diffusion manner.
[0046] A fuel cell system 1 includes one or more electricity
generating elements (or electrical generators) 3. The electricity
generating element 3 generates electrical energy through an
electrochemical reaction of a fuel and an oxidant. In addition, the
fuel cell system 1 includes a fuel supplier 5 for supplying a fuel
to the electricity generating element 3, and an oxidant supplier 7
for supplying an oxidant to the electricity generating element
3.
[0047] In addition, the fuel supplier 5 is equipped with a tank 9
that stores a fuel, and a fuel pump 11 that is connected therewith.
The fuel pump 11 supplies fuel stored in the tank 9 with a pumping
power that may be predetermined.
[0048] The oxidant supplier 7, which supplies the electricity
generating element 3 with an oxidant, is equipped with one or more
pumps 13 for supplying an oxidant with a pumping power that may be
predetermined.
[0049] The electricity generating element 3 includes a
membrane-electrode assembly 17, which oxidizes hydrogen or a fuel
and reduces an oxidant, and separators 19 and 19' that are
respectively positioned at opposite sides of the membrane-electrode
assembly 17 and supply hydrogen (or a fuel) and an oxidant,
respectively. In one embodiment, the electricity generating
elements 3 are stacked to form a stack 15.
[0050] The following examples illustrate the present invention in
more detail. However, the present invention is not limited by these
examples.
EXAMPLE 1
[0051] A carbon-cloth electrode substrate was fabricated by weaving
a polytetrafluoroethylene yarn with an average diameter of 100 nm
and a carbon fiber in a ratio of 5:95 wt %.
[0052] Next, a catalyst composition for an anode was prepared by
mixing 88 wt % of a Pt-Ru black (Johnson Mafthey) catalyst and 12
wt % of NAFION/H.sub.2O/2-propanol (Solution Technology Inc.) in a
5 wt % concentration as a binder. A catalyst composition for a
cathode was prepared by mixing 88 wt % of a Pt black (Johnson
Matthey) catalyst and 12 wt % of NAFION/H.sub.2O/2-propanol
(Solution Technology Inc.) in a 5 wt % concentration as a binder.
They were respectively coated on the carbon clothe electrode
substrate to prepare an anode and a cathode.
[0053] Then, the anode, the cathode, and a commercially-available
NAFION 115 polymer electrolyte membrane were used to fabricate a
membrane-electrode assembly.
[0054] The membrane-electrode assembly was inserted between glass
fiber gaskets coated with polytetrafluoroethylene, and then between
two bipolar plates including a gas channel and a cooling channel
with a set (or predetermined) shape and compressed between copper
end plates, thereby fabricating a fuel cell system with a unit
cell.
EXAMPLE 2
[0055] A unit cell was fabricated according to the same (or
substantially the same) method as in Example 1 except for using a
polytetrafluoroethylene yarn with an average diameter of 1
.mu.m.
EXAMPLE 3
[0056] A unit cell was fabricated according to the same (or
substantially the same) method as in Example 1 except for using a
polytetrafluoroethylene yarn with an average diameter of 500
nm.
COMPARATIVE EXAMPLE 1
[0057] A unit cell was fabricated according to the same (or
substantially the same) method as in Example 1 except for including
an electrode substrate formed by immersing a carbon cloth made of
carbon fiber in a polytetrafluoroethylene resin solution.
[0058] Then, 1 M of methanol and dry air were injected into the
fuel cells according to Examples 1 to 3 and Comparative Example 1.
Based on their output measurements, the fuel cells according to
Examples 1 to 3 were found to have better fuel cell characteristics
as compared to that of Comparative Example 1.
[0059] While the present invention has been described in connection
with certain exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments, but, on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims, and equivalents thereof.
* * * * *